1. Field of the Invention
The invention relates to a sheath device with gradable stiffness and method that reduces or prevents buckling when inserted into a vascular tract.
2. Background Art
Endovascular surgery has developed as a form of minimally invasive surgery that is used to access many regions of the body through major blood vessels. Conventionally, a catheter is introduced through the skin into a large blood vessel such as the femoral artery or vein. Often, the catheter carries a radio-opaque dye that can be detected by X-ray or fluororscopic procedures. Endovascular surgery is becoming more widely used because it is minimally invasive and offers immediate advantages over more traditional, yet highly invasive surgeries.
Generally stated, a catheter is a tube that can be inserted into a body cavity, duct or vessel. Catheters typically allow drainage or the injection of a fluid or access by surgical instruments. Many uses require that the catheter be thin and flexible (a “soft” catheter or tube); in other cases it may be a larger solid tube—a “hard” catheter.
As used herein, (1) the term “sheath” refers to the outer covering of a guide wire. Unless the context dictates otherwise, it may be used interchangeably with the term “catheter,” and (2) the term “guide wire” refers to a long and flexible fine spring that is used to introduce and position an intravascular catheter. Conventionally, the catheter or sheath is often threaded over the wire—the wire may then be withdrawn, leaving the catheter in place, as taught by the Seldinger technique, a medical procedure that is used to obtain access to blood vessels and other hollow organs. Seldinger S1 (Catheter Replacement of the Needle in Percutaneous Arteriography; a New Technique). Acta Radiologica (5); 368-76 (1953).
During interventional vascular procedures, situations may arise where a catheter needs to be advanced through tortuous paths, in which it may be difficult to steer a guide wire or other interventional device along the interstices a vessel. For example, one area in the vascular geometry that causes issues related to advancing a device is the interface of the femoral and aortic vessels. During peripheral procedures, the entry location for devices is the femoral artery on the side of the body opposite the area of concern. The device must then pass over the femoral arch and into the opposite femoral artery. When the interventional devices used during the procedure advance towards such tortuous anatomy, buckling of the device often occurs at the femoral/aortic interface. Typically, conventional interventional devices tend to buckle under the axial force reaction of the tortuous vessel to the pressures of insertion. Buckling of the device often occurs proximal to the tortuous anatomy.
There are several reasons why this situation is difficult to overcome with current technology:
1. The geometry of a guide wire. A guide wire must have some flexibility to be able to steer through the vascular anatomy without dissecting a vessel. A guide wire is typically a small diameter wire (0.014″) and is pliable and soft. When the guide wire is advanced through any tortuous anatomy, due to the small size of the wire, the wire has little ability to resist buckling. The proximal section of the wire typically buckles, and very little if any force is transmitted to the distal end of the wire.
2. The flexibility of the guiding catheter or sheath. Guiding catheters and sheaths are conventionally made from reinforced extruded plastic tubing. These devices are soft and generally provide little resistance to buckling.
3. The intervention devices that are used during the procedure. The intervention devices (e.g. stent delivery systems and balloons) are pliable along their axial shaft, and easily buckle when an axial force is applied.
Most devices and techniques that are available do not provide a solution to the buckling that occurs when tortuous anatomy is encountered during a procedure. If a device can not be advanced through this tortuous anatomy, the procedure may not be able to be performed, and the outcome for the patient may be compromised.
It is known that when the leading edge of a sheath encounters a tight lesion, there is a loss of kinetic energy. Some approaches solve this problem by using a hydrophilic material that is applied to the sheath. The problem with this approach, however, is that the surgeon's hands tend to slip over the outside surface of the sheath.
Among the U.S. and foreign patent documents that were considered before filing this application are the following: EP131632; EP171682; WO98/5644; U.S. Pat. Nos. 5,599,326; 7,226,466; 7,273,487; 20060235502; 20060258987; 20060264907; 20070049899; 20080045895; 20080172037.